1. Field of the Invention
The present invention relates generally to an apparatus and method for manufacturing tubing and, more particularly, to an apparatus and method for manufacturing catheters having a simple or complex configuration by applying a nonextruded layer of polymer material over a core member.
2. Description of the Related Art
Medical tubing and catheters are widely employed for a variety of treatment and diagnostic procedures involving, for example, the administration of fluid medications and devices into a patient and the removal of fluids from the patient. In this application, the terms "catheter" and "medical tubing" will be used interchangeably to refer to the same structure.
The ultimate use for which medical tubing is designed requires that the tubing have certain physical characteristics. For example, a catheter must be sufficiently stiff or rigid to enable its insertion and movement through narrow body orifices and channels and, in some applications, must also be able to withstand a high bursting pressure. On the other hand, a catheter must be sufficiently soft and flexible so that it may readily conform to body shapes so as not to cause injury to the interior wall of a patient's vessel as it is advanced. In addition, a catheter must be of sufficient mechanical strength to resist tearing during normal use, such as when the catheter is removed against tissue resistance.
Catheters have been manufactured for several years by numerous methods. Mechanical performance requirements of catheters have increased over time because of new procedures, such as angioplasty and therapeutic and diagnostic neurological procedures. In these applications, it is desirable to have a catheter that varies in hardness along its shaft length. Conventional methods to meet this requirement consist of segmenting the wall of the catheter with plastics having varying hardness. The segments are generally individual tubes bonded together, or segments of varying hardness within a laminated-type construction. The transition from hard to soft polymer in these types of constructions is abrupt and may require many segments to achieve the desired hardness transition, which complicates manufacture.
Other methods for manufacturing catheters having varying hardness along the length of the catheter have been disclosed. For example, U.S. Pat. No. 4,385,635 (RUIZ) and U.S. Pat. No. 5,085,649 (FLYNN) each discloses a catheter tubing having tapered resin layers of different hardness. The tapered layers are formed by a controlled extrusion process using, for example, a bi-orifice extrusion head with a controlled discharge rate to keep the combined thickness of the respective layers constant. Because these methods rely on an extrusion process to form the tapered layers, they are relatively expensive to implement and are difficult to control in a manner that achieves an optimum hardness transition over the length of the catheter. The tapered layers also tend to make it difficult to incorporate reinforcement filament into the catheter during manufacturing.
Catheters are often employed for diagnostic procedures that require sensors to be placed within body orifices. An example of one such catheter 200 is shown in FIGS. 15 and 16. In this conventional catheter, a tubing 201 is first formed using a conventional extrusion process or the like. A hole 202 is then formed in the wall 203 of the tubing 201. A conductor wire 204 is then inserted through the lumen of the tubing 201 and out through the hole 202 (or vice versa). A surface electrode 205 in the form of a metal band is electrically connected to the conductor wire 204 and placed over the hole 202 around the outer surface of the catheter 200. The surface electrode 204 functions as a sensor.
This conventional sensor arrangement for catheters has a number of disadvantages. The conductor wire 204 is placed within the lumen of the catheter 200, thereby interfering with the passage of fluids and the like through the lumen. The process of assembling the conductor wire 204 and surface electrode 205 to the catheter 200 is quite difficult since the catheter 200 is formed separately from the sensor and conductor wire.
Nylon powders are commercially available for use as painting or chrome alternatives to eliminate harmful emissions and waste products during metal plating operations, for example. These nylon powders have been applied using electrostatic/baking applications that produce films over metal substrates and the like having a thickness in the range of 0.004 to 0.050 inches. In conventional applications of the powders, the substrate is grounded, the plastic powder is charged and applied with a spray or fluidized bed exposure, and then the powder-coated substrate is baked. This known technology has not previously been adopted in a catheter manufacturing process.